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Drag and Drop for UI elements
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Description

In Blender, we have had drag and drop support for dragging content such as images onto objects, and 3d content into 3d views. However, we've always lacked the ability to drag the UI elements themselves.

This would be good to finally address.

This would mean we can get rid of these re-ordering buttons, which are slow because you can only move items one line at a time:

To move an item up by 10 lines, you have to click this button 10 times! This gets ridiculous if you have to move something 200 items up or down a list.

Even worse, in some cases we make users open a menu to move items one section at a time:

We should get rid of these buttons and menu entries, and just let users directly drag UI elements instead.

We already do this in the Properties Editor when re-ordering panels:


However, we can do this many more places, wherever we have the need for users to be able to re-order something.

Examples:

Animations are slowed down to show the animations more clearly.

Tabs:

Lists:

Animation

To support this nicely, we should use animation to make items move out of the way, and to let the current items follow the cursor. This makes the UI feel physical and dependable, and you won't get any sudden surprises when you let go of your drag action, and the UI elements suddenly re-order themselves.

This kind of thing has a few implications how we draw some UI elements.

In Blender we still have the fairly unique advantage that we are drawing the UI using the GPU, which facilitates creating beautifully smooth animations and transitions. We just need to take advantage of this more, just as we do with region overlapped area regions:

Related Tasks

D4071: New Drag & Drop System [WIP]

Details

Type
Design

Event Timeline

William Reynish (billreynish) lowered the priority of this task from Needs Triage by Developer to Normal.Jul 29 2019, 6:58 PM
William Reynish (billreynish) changed Type from Bug to Design.
William Reynish (billreynish) updated the task description. (Show Details)

I'm not fond of animations especially for the 'UI list' case - I think drawing a dotted line where the item is going to be inserted is more efficient and straightforward (as most painting programs do it in their 'layers' list) - seeing items shift around disorientates me when I'm trying to precisely move a specific item to a location I'm targeting - when suddenly that visual target slides around, I'm not sure where to drop the thing anymore. Maybe that's just my brain ? Quite a few interfaces do this (off the top of my head Discord does this with its channel list, & last I checked Android UI framework kind of enforces it too) and I find it quite disturbing. They do make more sense in a grid view (2D) though, because the order of items is not necessarily as obvious as in a list (1D).
Other than that, obviously in full agreement of the proposal.

Regarding vertex groups and other items that are in UI lists - also your example shows clearly a problem that would be probably better addressed in Outliner. A typical list of vertex groups on a character has a length of at least 20, and that is for very simple rigs. Then comes the problem of dragging to the border and then starting some auto-scroll - which is perceptually probably very confusing. I don't say this won't happen in Outliner, but there is simply much more space by default to do these things. So the question is, why not to get rid of the lists instead of trying to improve something that won't work also with this improvement.

Good point. I know of a way certain programs address that : they allow for splitting the list in two : one at the top, another at the bottom. Moving an item a long way is then just a matter of scrolling to the right place in the first 'pane' so to say, and then dragging the item from the second pane into the first one.

@Vilem Duha (pildanovak) that is irrelevant to improving drag and drop in Blender. We use this UI in many places, not just for Vertex Groups.